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Dec
27
answered Using HMAC to secure a “widget”
Dec
27
comment Off-the-record communication
@RamRachum: No, because that would lose the deniability property we wanted in the first place: for a given $W' = W \oplus SHA(m) \oplus SHA(m')$, finding $Y'$ and $Z'$ such that $W' = H(Y' + Z')$ (for any meaning of $+$) would require breaking the preimage resistance of $H$.
Dec
27
reviewed Approve Off-the-record communication
Dec
25
comment Off-the-record communication
@RickyDemer: Good point. $\hspace{400px}$ But honestly, what's the deal with $\hspace{300px}$ the random $\hspace{240px}$ MathJax spaces, anyway? $\hspace{200px}$ $\hspace{200px}$ You know it doesn't really look the same $\hspace{100px}$ to anyone who doesn't have the exact same browser and fonts as you $\hspace{250px}$ anyway, right?
Dec
25
answered Why is time-lapse cryptography not popular?
Dec
24
revised Hash function based on pseudorandom functions and security
edited tags
Dec
24
revised A situation where security by obscurity might be the best solution - or am I wrong?
edited tags
Dec
24
revised Acceptable assumptions when proving security
edited tags
Dec
24
revised Secure use-cases of block cipher with 64-bit block size
edited tags
Dec
24
revised Composition of block ciphers and 3DES
edited tags
Dec
24
revised Have these compositions of block ciphers the same security?
edited tags
Dec
24
revised Is a small size block cipher usable?
edited tags
Dec
22
comment Keeping IV secret for AES CFB mode
...unless they never reuse the key for two different messages; in that specific case (and only in that case) using a constant IV is safe.
Dec
22
reviewed Satisfactory Why is sharing the seed and using SecureRandom “deterministically” so bad?
Dec
22
comment Two-dimensional S-Box
If $S'$ and $S''$ are the same S-box, why do you use two different symbols to represent them?
Dec
22
comment Two-dimensional S-Box
I'm not sure I understand what you're asking. If $S_1$ and $S_2$ are $n$-bit-to-$n$-bit S-boxes, then the function $S_{12}$ defined as $S_{12}(x) = S_2(S_1(x))$ can also be represented as an $n$-bit-to-$n$-bit S-box, so combining S-boxes like that generally doesn't gain you anything.
Dec
21
answered hill cipher encryption way 1x3 plaintext matrix
Dec
21
revised ECB weakness and its exploitation
edited tags
Dec
21
comment ECB weakness and its exploitation
You should be able to find out the length of A, at least rounded down to a multiple of 16 bytes, by changing your message and seeing which ciphertext block is the first one that changes. Can you then figure out how to get the exact length of A in bytes? (Hint: What happens to the ciphertext if A is, say, 15 bytes long, and you change the first byte of your data? What if you change the second byte instead?)
Dec
21
answered ECB weakness and its exploitation